December remains rare as a baby name, but parents do sometimes use it --33 times in 2011. It probably helps that Ember, a top 1000 name, can be its nickname. The same can be said of November, but Nova would probably be the go-to nickname for that one.
Season is another word name turned rare baby name, used only 6 times in 2011, but it would make a great alternative to overused Christmas names, while still being appropriate all year long.
Angela is being heard less these days, but also consider Angelia, Ingela, Angelus and Argelia. You might want to avoid Angel for a few reasons.
Rudolpha at first seems to scream "Rudolph the Red-Nosed Reindeer," but it actually seems very sweet and wholesome. It's also good for parents looking for frilly, feminine names with masculine nicknames: Rudy.
Emmanuelle could make a great alternative for Noelle this time of year, and it has a religious meaning fitting for Christmas.
Natale is much less heard than Natalie, Natalia and Natasha, which all share meanings.
Shepherd is a nice name loosely connected to Christmas, but Shepherdess is a great female spin on the occupation baby name, brought to my attention recently.
Poinsettia is the Christmas plant, and while names like Rose and Lily remain eternally popular, rare plant names never get used.
Cardinal is the poinsettia of the bird world. The Christmas bird, since its bright red stands out dramatically in the snow.
Garland is one part Judy Garland, one part Christmas garland, and one part surname.
Carol hasn't ranked in a while, yet remains very Christmas appropriate. Caroline seems to be more in favor.
Tuquoise and Fairuza may seem like summer stones, but they're December's birth stones.
Evangeline (and Evangelia, Evangelista and Evangela) are the classy and gorgeous girls of the season.
Winter is doing very well and getting more popular than ever, but Snow is picking up attention as a middle name, and North is becoming a little more popular for boys in the first and middle spot.
Eirawen and Gwyneira are not to be missed if the meaning "snow white" is perfect for you.
Aspen is popular for girls, but not for boys.
Nicolai is the rare variant of Nicholas, perfect for honoring none other than St. Nick himself.
Vesper has been in the news lately, but the "evening star/evening prayer" meaning is perfect for this time of year.
Eve, Gioia, and Felicity/Felice/Felicienne/Feliciana are other options.